You can be "attracted" to a person, or to a type, for many reasons. In principle, what socionics says is that persons of your dual type are those with whom a close, longer-term relationship is the most favorable, comfortable, successful, etc - all other things being equal.
Other texts say that, indeed, you are attracted to your dual the moment you meet them -- well, I don't know that that's always the case.
Looking back at my own life, I have seen the pattern that I used to be attracted to, and inclined to start relationships with, ENFjs, which was sort of counter-productive.